We need more details in order to help you. Are you starting them indoors? Are you using bottom heat? Starting mix? Peat pots or pellets? Do you have a light set-up? Have you read the FAQs for growing from seed? Can you post photos(not necessary but helpful)?

Here is a link that might be useful: Growing from seed FAQs

Agree that much more info is needed. However based on the info so far the most likely explanation is damping-off. The primary cause is too wet and too warm growing conditions.

Dave

Here is a link that might be useful: Damp-off FAQ

Thanks Dave and noinwi

I'll check out those links.

Appreciate your help.

Take the dome off after you get sprouts. Remember, moist, not wet ... use a small fan on low to help harden your plants ...

Here is a link that might be useful: Starting Seeds Indoors